Stocks plunged on Wall Street today. U.S. stocks saw their biggest sell-off in six months. The Dow fell 831 points, which is a 3 percent decline. Here to talk about exactly what happened is NPR's John Ydstie. Hey, John.

JOHN YDSTIE, BYLINE: Hi, Ailsa.

CHANG: So what made the market plummet today?

YDSTIE: Yeah. It was a tough day, and a number of things contributed. Let's start with interest rates. Rates on government bonds have been rising rapidly over the past few weeks. That's made the market nervous. In fact, this is the fifth straight day of losses for the S&P 500. Rising interest rates make stocks less valuable, and there's concern in the market about just how high rates will go. The Federal Reserve has said it will continue to raise rates gradually, and it has suggested it will stop raising benchmark rates between 3 and 3 1/2 percent. So it still has a way to go to get there.

CHANG: So the way I understand it, the Fed usually raises rates to stave off inflation, right?

YDSTIE: Right.

CHANG: Are there fears of inflation right now?

YDSTIE: Well, Federal Reserve chair Jerome Powell has said recently he doesn't see inflation accelerating. However, the economy is clearly very strong, and the unemployment rate is at a 50-year low, so there's concern in the markets that wages will begin to rise more rapidly, and that could create inflation pressures.

CHANG: But you're saying the economy remains strong, so shouldn't that be good for the stock market?

YDSTIE: The economy is strong in the U.S. and most commentators are saying today's sell-off is not the end of the bull market and stocks here. But while the U.S. economy remains strong, Europe has cooled a bit, as have emerging markets. And the IMF gave a less-than-glowing assessment of the global economy this week - less glowing than it did just a few months ago. And, of course, there are concerns about global trade being disrupted by a trade war between the world's two biggest economies, the U.S. and China, and that hurts stocks.

CHANG: Are there any particular areas of the market that have been hurt by the sell-off?

YDSTIE: Well, virtually, all sectors of the market sold off today, wiping out all the stock gains since midsummer. But the tech sector has been hit the hardest, and it's been one of the foundations of this bull market. In fact, the tech-heavy Nasdaq index lost 4 percent of its value today, and the S&P 500, which also has a lot of tech, lost 3 1/3 percent. So it's been a very tough day for tech.

CHANG: A very tough day, but is this just the beginning of a long downward trend for the market?

YDSTIE: Well, most analysts I heard from today don't think so. Some said the selling toward the end of the day, which took the Dow down from around 500 points to 830 points down, was due to machine trading driven by algorithms that reached levels that call for selling. Given the strength of the U.S. economy and the likelihood of continued high levels of profits in American businesses, it's difficult to believe the market will continue to melt down.

But we are at a point where investors are looking out over the horizon nine months to a year from now and wondering whether the Fed will have raised rates so much that the economy gets pushed into recession. We're also getting to a point where bond yields are high enough that the interest rates they're paying is starting to compete with stocks. We'll see how foreign markets absorb this tomorrow. And then the U.S. market will have another crack at it, and we'll see what happens.